linux-kernel - Re: [Kernel Bug] KASAN: slab-use-after-free Read in __blkcg_rstat

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <l55sz3sgogoyniecolvzscjamxqrxlzgk7w7scds3tt42z6atj@nrfvjqg2agib>
Date: Tue, 3 Feb 2026 13:53:40 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Ming Lei <ming.lei@...hat.com>
Cc: 李龙兴 <coregee2000@...il.com>, 
	syzkaller@...glegroups.com, tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk, 
	cgroups@...r.kernel.org, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	yukuai@...as.com
Subject: Re: [Kernel Bug] KASAN: slab-use-after-free Read in
 __blkcg_rstat_flush

On Tue, Feb 03, 2026 at 07:11:11PM +0800, Ming Lei <ming.lei@...hat.com> wrote:
> RCU supports this way, here is just 2-stage RCU chain, and everything
> is deterministic.

The time when RCU callback runs is noisy, moreover when chained after
each other.
(I don't mean it doesn't work but it's debugging/testing nuisance. And
it also looks awkward.)

> I thought about this way, but ->lqueued is lockless, and in theory the `blkg_iostat_set`
> can be added again after WRITE_ONCE(bisc->lqueued, false) happens, so this way looks
> fragile.

Right, I brushed up on the cycles from the commit 20cb1c2fb7568
("blk-cgroup: Flush stats before releasing blkcg_gq") and it'd be a step
back.

Does anything prevent doing the each-cpu flush in blkg_release() (before
__blkg_release())?

Regards,
Michal

Download attachment "signature.asc" of type "application/pgp-signature" (266 bytes)